(1) Field of the Invention
The present invention relates to a multilayer board that is highly tamper-resistant, and a design apparatus, method, an program for the multilayer board.
(2) Description of the Related Art
Recently, contents of various fields such as music, still images, moving images, and games have been distributed as digital information thanks to the development of digital information technology and widespread use of digital information communication infrastructures.
Meanwhile, there has always been the fear that the digital contents are acquired by an unauthorized party by means of interception of communications, wiretapping, or disguise, and that the acquired contents are tampered or copied illegally in recording media. It is therefore very important in protecting the right of copyright owners or profits of distributors that any devices to deal with such contents are tamper-resistant, namely, difficult to unauthorized accesses.
Various conventional security technologies are available to make a communication medium tamper-resistant. For example, in a challenge-response type mutual authentication, a transmitting side and a receiving side authenticate themselves by exchanging a random number and a response value, and only when the authentication succeeds, security data protected by copyright is allowed to be transferred between them.
Not only communication media but also multilayer boards containing semiconductors for reproducing contents require tamper-resistance. This is because information passing signal lines on multilayer boards may be probed and reproduced. To make multilayer boards tamper-resistant, therefore, signal lines, which transfer security signals (contents, signals used for authentication, etc.), need be tamper-resistant.
The following methods are known to be used for making such signal lines on multilayer boards tamper-resistant.    (1) All functions contained in a multilayer board are achieved by a one-chip IC so that any security signal does not transferred directly on the multilayer board.    (2) Encryption and decryption processes are embedded into components on the multilayer board. More specifically, a logic for encrypting security signals is embedded into a component for outputting security signals, and a logic for decrypting security signals is embedded into a component for inputting security signals.    (3) Signal lines for transferring security signals on the multilayer board are coated with resin.
Each of the above three methods, however, is to increase the cost since in the first method, existing ICs cannot be used, in the second method, logics for encryption and decryption need be embedded into corresponding components, and in the third method, resin is required as an additional material.